This invention relates generally to injection molding and more particularly to a heated nozzle for conveying melt from an inlet to a number of spaced gates, each leading to a different cavity.
Heated nozzles for multi-cavity molding such as by edge gating are well known in the industry. For instance, the applicant's U.S. Pat. No. 4,663,811 which issued May 12, 1987 discloses heated nozzles with a variety of different gate configurations, one of which is edge gating. While these previous arrangements are entirely satisfactory for some applications, in other cases they do not provide sufficient heat and/or structural strength or the area adjacent the cavities is too difficult to cool. As is well known, with the continual development of more and more difficult to mold materials it is increasingly important to provide more heat closer to the gate area. There are various arrangements to do this for a single central gate, such as the hop tip seal shown in the applicant's U.S. Pat. No. 4,450,999 which issued May 29, 1984 or the circular heating element porton shown in the applicant's Canadian patent application serial number 578,973 filed Sept. 30, 1988 entitled "Injection Molding Nozzle Having Nose Portion with Heating Element Encircling the Bore and Method". However, it is much more difficult to provide additional heat to the areas of the gate in a configuration where a number of gates are spaced around or along the periphery of the nozzle. Also, with some cavity and gate configurations it is difficult to provide the mold with sufficient strength to withstand the repeated impact of the clamp force and the high injection pressure. In other words, if only a thin portion of the cavity plate is provided between the front end of the nozzle and the parting line, the mold will often eventually fracture resulting in shut down of the system. An early configuration in which a heater cast having spaced nozzle portions for edge gating is disclosed in the applicant's U.S. Pat. No. 4,094,447 which issued June 13, 1978.